The method relates to a device and a method for producing a metallic contact structure for electrically contacting a photovoltaic solar cell.
A photovoltaic solar cell represents a planar semiconductor element, in which via incident electromagnetic radiation a separation of charge carriers is generated, so that a potential develops between at least two electric contacts of the solar cell and electric power can be tapped from the solar cell by an external circuit connected thereto via contacts.
Here, the charge carriers are collected via metallic contact structures so that by contacting these contact structures at one or more contact sites the charge carriers can be supplied to the external circuit. Typically, here metallic contact structures are applied on a surface of the solar cell during the production of said solar cell, frequently in a grid-like or double-comb shape, with the contact structures covering the surface of the solar cell like fingers so that the charge carriers are collected from all sections of the solar cell in a planar fashion by the contact structure and can be fed from there to an external circuit.
When the contact structures are applied on a surface of the solar cell, where electromagnetic radiation shall impinge the solar cell, the contact structures must fulfill competing requirements: The contact structure shall cover a surface area of the solar cell as small as possible in order to minimize any loss from shadowing. Furthermore, in order to avoid electric loss the metallic contact structure shall exhibit a low contact resistance to the contacted semiconductor section of the solar cell, and on the other hand, the resistivity inside the contact structure shall be low.
Accordingly it is advantageous for the contacting structure arranged on the solar cell to exhibit an aspect ratio as high as possible, i.e. a high ratio of the height in reference to the width of the contact structure. This contact structure is embodied very small in this case so that low shadowing is achieved. Simultaneously the contact structure is embodied very high so that the cross-sectional area is large, accordingly the electrically resistivity perpendicular in reference to the cross-sectional area is low, and thus the charge carriers can be transported with little loss.
For the production of such contact structures it is known to apply the entire contact structure completely in a single step via serigraphy using a silver-containing paste. However, here wide contact structures develop, i.e. contact structures with a low aspect ratio, resulting in low conductivity and, due to their width, also in relatively high optic loss by shadowing the underlying semiconductor material of the solar cell.
Furthermore, it is known from U.S. Pat. No. 5,151,377 to generate a contact structure by a dispenser applying a paste, which comprises metal particles, via a dispensing opening onto a semiconductor substrate, with during the discharge the semiconductor substrate is moved in reference to the dispensing opening.
For the industrial production it is essential that the entire production process of the solar cell, particularly also the production of the contact structure, can be performed flawlessly and cost-effectively, without the effectiveness of the solar cell being considerably compromised by the production method selected.